Tetraalkylcyclobutane-1,3-diols can be important intermediates for producing a variety of polymeric materials which possess advantageous properties. For example, polyesters derived from dicarboxylic acids and 2,2,4,4-tetramethylcyclobutane-1,3-diol can possess higher glass transition temperatures, impact strength, weatherability, and hydrolytic stability in comparison to many other polyesters prepared from other commonly-used diols. Tetraalkylcyclobutane-1,3-diols can be prepared by the catalytic hydrogenation of the corresponding 2,2,4,4-tetraalkylcyclobutane-1,3-dione (I), as illustrated in FIG. 1 in which R is an alkyl group.
Typically, the hydrogenation of 2,2,4,4-tetraalkylcyclobutane-1,3-diones produces the corresponding 2,2,4,4-tetraalkylcyclobutane-1,3-diols as a mixture of cis and trans isomers. For example, U.S. Pat. No. 3,190,928 discloses the hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione using nickel- or ruthenium-based catalysts to produce 2,2,4,4-tetraalkylcyclobutane-1,3-diols with molar cis:trans ratios that can vary widely from about 0.5 to about 1.2. Also, catalysts that produce the most desirable ratio of cis:trans isomers may not give the best yields or highest rates of hydrogenation. The cis:trans isomer ratio of 2,2,4,4-tetraalkylcyclobutane-1,3-diols can influence important properties such as, for example, the glass transition temperature, impact strength, and crystallization rate of the polyester polymers prepared from them. A cis:trans ratio that varies widely, in turn, can give polyesters with inconsistent and/or undesirable properties. A process to isomerize 2,2,4,4-tetraalkylcyclobutane-1,3-diols, therefore, would be desirable in order to produce 2,2,4,4-tetraalkylcyclobutane-1,3-diols with consistent cis:trans ratios regardless of the hydrogenation catalyst used. Such an isomerization process also would enable the efficient production of polyesters from 2,2,4,4-tetraalkylcyclobutane-1,3-diols with properties that can be tailored to a variety of applications.